U.S. patent number 6,276,016 [Application Number 08/842,541] was granted by the patent office on 2001-08-21 for safety leg system for dock leveler.
This patent grant is currently assigned to Rite-Hite Holding Corporation. Invention is credited to Scott L. Springer.
United States Patent |
6,276,016 |
Springer |
August 21, 2001 |
Safety leg system for dock leveler
Abstract
A dock leveler including a deck pivotally mounted relative to a
loading dock, and a lip pivotally connected to the deck at the
front end for pivotal movement between a pendant position and an
extended position wherein the lip may engage the vehicle, at least
one leg member pivotally connected to the front end of the deck for
movement between a supporting position and a nonsupporting
position, and a leg control member pivotally attached to the front
end of the deck and adapted to engage the bed of the vehicle along
with the lip, and to maintain the leg member in a nonsupporting
position so long as the leg control member is carried on the bed of
the vehicle, the leg control member losing contact with a departing
vehicle before the lip loses contact with the vehicle, allowing the
leg member to return to a supporting position, such that downward
movement of the deck will be arrested in the event the vehicle
continues departing and the lip loses contact with the bed of the
vehicle with a load present on the deck.
Inventors: |
Springer; Scott L. (Whitewater,
WI) |
Assignee: |
Rite-Hite Holding Corporation
(Milwaukee, WI)
|
Family
ID: |
25287584 |
Appl.
No.: |
08/842,541 |
Filed: |
April 15, 1997 |
Current U.S.
Class: |
14/71.1; 14/69.5;
14/71.3 |
Current CPC
Class: |
B65G
69/2894 (20130101) |
Current International
Class: |
B65G
69/28 (20060101); B65G 69/00 (20060101); E01D
001/00 () |
Field of
Search: |
;14/69.5,71.1,71.3,71.5,71.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Neuder; William
Assistant Examiner: Singh; Sunil
Attorney, Agent or Firm: Marshall, O'Toole, Gerstein, Murray
& Borun
Claims
What is claimed is:
1. A dock leveler assembly for loading and unloading a vehicle
parked adjacent a loading dock, comprising:
a deck having a front end and a rear end, the rear end being
pivotally mounted relative to the loading dock to provide pivotal
movement of the deck between a stored position, and a range of
operative positions;
a hinge adjacent the front end of the deck;
a lip pivotally connected to the deck at the hinge for pivoting
between a pednant position and an extended position wherein the lip
may engage the vehicle;
a leg member pivotally connected to the deck on the same hinge as
the lip, and movable between a supporting position wherein the leg
member is disposed to arrest downward movement of the deck, and a
nonsupporting position.
2. The dock leveler assembly of claim 1, wherein a stop member is
disposed beneath the deck, and wherein the leg member includes a
proximal end pivotally mounted to the deck, and a distal end that
engages the stop member to arrest downward movement of the deck
with the leg member in the supporting position, and wherein the
distal end moves away from the rear end of the deck as the leg
member pivots to the nonsupporting position.
3. The dock leveler of claim 2, wherein the stop member includes a
plurality of stops disposed at different vertical positions.
4. The dock leveler assembly of claim 1, and including: a leg
control member pivotally connected to the deck at the hinge; and a
coupling between the leg control member and the leg member such
that the position of the leg control member relative to the deck
controls movement of the leg member between supporting and
nonsupporting positions.
5. The dock leveler assembly of claim 4, and including a coupling
between the lip and the leg control member, the coupling disposed
to engage the leg control member and move the leg control member to
a first position relative to the lip as the lip moves to the
extended position, and to allow the leg control member to move to a
second position relative to the lip as the leg control member and
the lip engage the bed of a parked vehicle.
6. The dock leveler assembly of claim 5, wherein the leg control
member is disposed and dimensioned to lose contact with the bed of
a vehicle departing from the loading dock before the lip loses
contact with the bed of the departing vehicle, the coupling between
the lip and the leg control member being disposed to allow the leg
control member to pivot from the second position to the first
position as it loses contact with the bed of the departing
vehicle.
7. The dock leveler assembly of claim 6, wherein the coupling
between the leg control member and the leg member provides movement
of the leg member from the supporting to the nonsupporting position
as the leg control member moves from the first position to the
second position; and vice versa.
8. The dock leveler of claim 1, and including a pair of leg members
pivotally connected to the deck at the hinge and connected together
by a strut member.
9. A dock leveler assembly for loading and unloading a vehicle
parked adjacent a loading dock, comprising:
a deck having a front end and a rear end, the rear end being
pivotally mounted relative to the loading dock to provide pivotal
movement of the deck between a stored position, a preparatory
position, and a range of operative positions;
a lip pivotally connected adjacent the front end of the deck for
pivoting between a pendant position and an extended position as the
deck reaches the preparatory position, the lip being disposed to
engage the vehicle in the extended position;
a leg member pivotally connected adjacent the front end of the
deck, and movable between a supporting position wherein the leg
member is disposed to arrest downward movement of the deck, and a
nonsupporting position, the leg member including a distal end and a
proximal end, and disposed such that the distal end moves away from
the rear end of the deck as the leg member pivots to the
nonsupporting position;
a leg control member pivotally connected adjacent the front end of
the deck, and coupled to the leg member such that the position of
the leg control member relative to the deck controls movement of
the leg member between supporting and nonsupporting positions;
and
wherein the lip, leg control member, and leg member are pivotally
attached to a common hinge on the front end of the deck.
10. The dock leveler assembly of claim 9, wherein the leg control
member is coupled to the lip such that movement of the lip to an
extended position moves the leg control member to a first position
relative to the lip, and wherein the leg control member moves to a
second position relative to the lip as the deck pivots downward
from the preparatory position and the leg control member engages
the vehicle.
11. The dock leveler assembly of claim 10, wherein the leg member
is coupled to the leg control member such that movement of the leg
control member from the first position to the second position moves
the leg member from the supporting position to the nonsupporting
position, and vice versa.
12. The dock leveler assembly of claim 11, wherein the leg control
member is dimensioned to lose contact with a vehicle departing from
the loading dock before the lip loses contact with the vehicle, the
leg control member moving from the second position to the first
position upon losing contact with the vehicle.
13. A dock leveler assembly for loading and unloading a vehicle
parked adjacent a loading dock, comprising:
a deck having a front end and a rear end, the rear end being
pivotally mounted relative to the loading dock to provide pivotal
movement of the deck between a stored position and a range of
operative positions;
a lip pivotally connected to the deck adjacent the front end, the
lip including a main section that pivots between a pendant position
and an extended position wherein the main section may engage the
vehicle, and a sensor section that pivots between a pendant
position, a first position wherein the sensor section may engage
the vehicle, and a second position between the first position and
the pendant position;
a leg member pivotally connected to the deck adjacent the front
end, and movable between a supporting position wherein the leg
member is disposed to arrest downward movement of the deck, and a
nonsupporting position in response to movement of the sensor
section of the lip from the first position to the second position,
the sensor section having a length shorter than the main section of
the lip such that the sensor section disengages from the vehicle
before the main section loses contact with the vehicle as the
vehicle moves away from the loading dock, such disengagement
allowing the leg member to return to a supporting position before
the main section loses contact with the vehicle;
wherein the main section, the sensor section and the leg member are
pivoted on a common hinge on the front end of the deck.
14. A dock leveler assembly for loading and unloading a vehicle
parked adjacent a loading dock, comprising:
a deck having a front end and a rear end pivotally mounted relative
to the loading dock to provide pivotal movement of the deck between
a stored position and a range of operative positions;
a header member attached across the front end of the deck;
a lip pivotally connected to the deck forward of the header member
for pivoting between a pendant position and an extended position
wherein the lip may engage the vehicle;
a leg member pivotally connected to the deck at least as forward as
the header member, and movable between a supporting position
wherein the leg member is disposed to arrest downward movement of
the deck, and a nonsupporting position, the leg member including a
distal end, and disposed such that the distal end moves away from
the rear end of the deck as the leg member pivots to the
nonsupporting position.
15. A safety leg assembly for a dock leveler for loading and
unloading a vehicle parked adjacent a loading dock, the dock
leveler including a deck having a front end and a rear end
pivotally mounted relative to the loading dock to provide pivotal
movement of the deck between a stored position and a range of
operative positions, and a lip pivotally connected to the deck
adjacent the front end for pivoting between a pendant position and
an extended position wherein the lip may engage the vehicle, the
safety leg assembly comprising:
a leg control member adapted to be pivotally connected to the deck
adjacent the front end for pivoting between a pendant position, a
first position wherein the leg control member may engage the
vehicle, and a second position between the first position and
pendant position;
a leg member adapted to be pivotally connected to the deck adjacent
the front end, and movable between a supporting position wherein
the leg member is disposed to arrest downward movement of the deck,
and a nonsupporting position in response to movement of the leg
control member from the first position to the second position, and
vice versa;
the leg control member having a length shorter than the lip such
that the leg control member disengages from the vehicle before the
lip loses contact with the vehicle as the vehicle moves away from
the loading dock, such disengagement allowing the leg member to
return to the supporting position before the lip loses contact with
the vehicle;
wherein the leg control member and the leg member are adapted to be
pivoted on a common hinge with the lip on the front end of the
deck.
16. The safety leg assembly of claim 15, wherein the leg control
member is adapted to be coupled to the lip, such that movement of
the lip from the pendant to the extended position moves the leg
control member from the pendant to the first position.
17. A safety leg assembly for a dock leveler for loading and
unloading a vehicle parked adjacent a loading dock, the dock
leveler including a deck having a front end and a header member
extending across the front end and a rear end pivotally mounted
relative to the loading dock to provide pivotal movement of the
deck between a stored position and a range of operative positions,
and a lip pivotally connected to the deck adjacent the front end
for pivoting in a first direction between a pendant position and an
extended position wherein the lip may engage the vehicle, the
safety leg assembly comprising:
a leg member adapted to be pivotally connected to the deck at least
as forward as the header member and including a distal end, and
adapted to move such that the distal end moves in the first
direction as the leg member moves between a supporting position
wherein the leg member is disposed to arrest downward movement of
the deck, and a nonsupporting position, said movement in the first
direction being adapted to be responsive to movement of the lip
from the pendant position to an extended position.
Description
FIELD OF THE INVENTION
The invention is directed generally to dock levelers, and more
particularly to a dock leveler exhibiting enhanced protection
against uncontrolled free fall.
BACKGROUND OF THE INVENTION
Dock levelers are commonly used at loading docks for the purpose of
bridging the gap between a vehicle parked adjacent the loading dock
and the loading dock itself. Typically, the vehicle will back up
into a parked position wherein the rear of the vehicle engages
bumpers disposed on the face of the building and intended to
protect both the building and the rear of the vehicle from impact
or defacement. With the vehicle backed against the bumpers, a gap
still exists between the loading dock and the truck. The dock
leveler is intended to bridge this gap.
Typically, the loading dock will be formed with a pit within which
framing for the dock leveler is housed. The leveler itself
comprises a deck pivotally attached at its rear end relative to the
loading dock, usually to the framing. The deck is movable between a
stored or "cross-traffic" position wherein the deck is even with
the warehouse or building floor on either side of the pit, and a
range of operating positions to accommodate various vehicle
elevations. The stored position is referred to as a "cross-traffic"
position since traffic moving in the warehouse can move over the
deck easily as it forms an extension of the surrounding floor. At
the front end of the deck, adjacent the parked truck, is a lip
pivotally connected to the front end of the deck for movement
between a pendant, or stored position and an extended position
wherein the lip bridges the gap between the deck and the bed of the
parked vehicle. With the leveler in this bridging configuration,
fork trucks or personnel can pass between the loading dock and the
bed of the parked vehicle for the purpose of loading and unloading
the vehicle. As the vehicle is loaded or unloaded, and as the fork
truck passes on and off of the vehicle, differing weights are
exerted on the vehicle's suspension. As a result, the vehicle will
typically move up and down throughout the loading or unloading
procedure. The pivotal connection of the deck of the dock leveler
allows the leveler to track this up and down movement of the
vehicle.
In operation, the deck is first raised from the cross-traffic
position (with the lip pendant) to a raised preparatory position.
The power to raise the deck is provided either by springs (in the
case of a so-called "mechanical leveler") or by a hydraulic
cylinder or other actuator disposed between the framing and the
deck. In a mechanical leveler a "holddown" device normally holds
the leveler down against the upward bias of the springs. The
holddown may be released to raise the deck by pulling the unit's
main pull chain. Once the deck reaches the preparatory position,
the lip is extended from its pendant position to an extended
position. Subsequent downward rotation of the deck places the lip
on the bed of the vehicle so as to bridge the gap between the dock
and the vehicle. In a hydraulically-powered leveler, or one powered
up by a different actuator, gravity provides the force necessary to
rotate the leveler downward, while a mechanical leveler requires
the weight of dock personnel to "walk down" the leveler to a
position wherein the lip rests on the bed of the vehicle. As the
vehicle moves up and down during loading or unloading, the leveler
pivots up and down to maintain proper contact with the vehicle.
Since dock levelers are capable of pivoting in this manner, they
preferably also include some means for preventing uncontrolled free
fall of the deck in the event that the vehicle departs while a fork
truck or other load is still disposed on the deck. Departure of the
vehicle with a load still on the deck is typically referred to as
"premature" or "unscheduled" since proper safety procedures require
that the deck be unloaded before a vehicle departs. If premature
departure were to occur without any means of free fall protection,
such premature departure of the vehicle would mean that the lip was
no longer in contact with the vehicle, and thus that the heavily
loaded deck was effectively unsupported, and it would thus pivot
downwardly through its full range of motion until it engaged the
pit below. Given that a typical operating range for dock levelers
is from 10 inches above dock height to 10 inches below dock height,
it would be possible for a fork truck disposed on the leveler in
such a situation to fall as much as 20 inches. The violent contact
between the falling deck and the pit, as well as the substantial
pitch at which the deck would then be disposed, could lead to
undesirable results, such as the fork truck falling off the deck or
goods or personnel being damaged or injured.
Different types of levelers may include different types of free
fall protection intended to minimize the distance through which the
deck may free fall before such downward movement is arrested. In
the case of hydraulic levelers, the deck is powered through its
range of motion by means of a hydraulic cylinder disposed between
the underside of the deck and the pit below. To protect against
free fall, the hydraulic cylinder typically includes a velocity
fuse. The velocity fuse is intended to lock the hydraulic cylinder
against further movement in the event that the deck achieves a
certain velocity. Accordingly, if free fall begins to occur and the
deck reaches this velocity, the hydraulic cylinder will be locked,
and prevent the deck from further downward movement. Mechanical and
other types of levelers, on the other hand, typically include
so-called safety legs to limit free fall distance. An example of
one type of safety leg mechanism is shown in the prior art FIGS. 2
and 3. The safety leg SL depends from the bottom of the deck and is
adapted to engage a pedestal P disposed in the pit. Contact between
the end of the leg SL and the pedestal P will arrest downward
movement of the deck indicated as D. Thus, if a vehicle prematurely
departs with a load on the deck, the deck will only "free fall" a
limited distance--until the legs SL engage pedestal P. The legs SL
typically remain in a supporting orientation for this purpose. For
situations where the bed of the truck is significantly lower than
dock height, the legs may be retracted rearwardly by a retracting
mechanism R to allow the deck to angle downwardly below dock
without the safety leg engaging the first stop S1 on the pedestal.
To protect against free fall with the deck in a below-dock
configuration, a second stop S2 is provided on the pedestal. The
safety leg L is biased by a biasing member B, in this case a
spring, toward the vertical position shown in FIG. 2. Accordingly,
if the leveler is initially disposed below dock with the legs
retracted and then is raised above dock by virtue of weight being
removed from the truck and the vehicle suspension raising the
leveler, the safety leg SL will return to the vertical orientation
shown in FIG. 2.
While the safety leg configuration, and other similar safety leg
configurations, provide the advantageous function of preventing
substantial free fall in the event of premature or unscheduled
departure of the vehicle with a load on the deck, they are not
without their own limitations. One such limitation to previous
safety leg configurations is shown if FIG. 3. In the circumstance
shown in FIG. 3, the leveler is in a position wherein the safety
leg SL engages the stop S1 on the pedestal P, thus preventing
further downward movement of the leveler. As the fork truck moved
onto the vehicle bed, however, the weight of the fork truck pushed
the vehicle down further. The lip L was able to track this downward
movement of the vehicle, since engagement of the safety leg SL with
the stop S1 does not limit rotational movement of the lip L. The
deck D, however, was prevented from moving to a lower position. The
steep angle of the lip L may prevent the fork truck from being able
to drive back up that slope and onto the deck D, or may at least
cause a jarring collision between the lip and the fork truck. In
the former circumstance, the fork truck may get trapped on the
vehicle. This condition, typically referred to in the industry as
"stump out" is an inconvenience, and represents a potential safety
hazard to the fork truck operator who does not notice the
significant angle of the lip. In addition, damage to either the
lip, the leveler or the fork truck may occur as the fork truck
attempts to drive back up the inclined lip. As the function of
safety legs is otherwise very desirable, it would be advantageous
to be able to provide a safety leg system that does not suffer from
the disadvantages of stump out.
At least two attempts have been made in the prior art to address
this issue. Both U.S. Pat. Nos. 3,995,342 and 5,440,772 include
sensors that engage the bed of the vehicle along with the lip. In
both cases, the sensor is shorter than the lip such that, in the
event the vehicle prematurely departs, the sensor loses contact
with the bed of the vehicle before the lip loses contact with the
vehicle. When the sensor is in contact with the vehicle, the safety
legs are retracted such that they are in a nonsupporting position.
Upon the sensor losing contact with the bed of the vehicle, the
safety legs are restored to a supporting position such that they
would arrest downward movement of the leveler. Thus, when the
vehicle departs, the sensor first loses contact with the vehicle
moving the legs to a supporting position, and then the lip loses
contact with the vehicle. This loss of contact between the lip and
vehicle, however, does not result in substantial or uncontrolled
free fall, since the legs have been restored to a supporting
position. While these systems theoretically address the stump out
problem, neither system proved to be workable in practice. For
example, the system of the '342 patent includes a feature wherein
the lip is latched into its extended position, and only could be
unlatched by contact with the vehicle bed. Such a feature is
problematic and potentially dangerous in the situation where the
deck is raised and the lip is latched out, and then the deck is
walked down without ever engaging a vehicle. As a result, the
latched-out lip presents an obstacle and potential point of damage
for a vehicle that backs into the loading dock while it is still
latched in position. Another danger is that, in this scenario, if a
fork truck were to drive onto a leveler with a latched-out lip, the
leveler would rapidly rotate downward since the safety legs would
not be in a supporting position. Moreover, both of these prior art
systems included several pivot points, for the lip, the sensor, and
the legs, and fairly complex mechanisms between these three members
for the purpose of providing the desired safety leg function
without stump out. The tolerances required to achieve proper
functionality were difficult to achieve, leading to inconsistent
function, as well as difficulty in manufacturability of these
systems. The complex nature of the actuating mechanisms also led to
increased expense for these systems.
SUMMARY OF THE INVENTION
It is therefore the primary aim of the present invention to provide
a safety leg system for a dock leveler that avoids the drawbacks
associated with previous such systems.
In accordance with the aim, it is a primary object of the invention
to provide a safety leg system that minimizes uncontrolled free
fall of a dock leveler in the event of premature vehicle departure,
but that also avoids the problem of stump out.
A further object is to provide a dock leveler with a safety leg
assembly that is simple to implement and reliable and repeatable in
operation.
A related object is to provide dock leveler with a safety leg
assembly that has enhanced manufacturability as compared to
previous systems.
In accordance with these and other object of the invention, there
is provided a dock leveler comprising the conventional features of
a deck having a front end and rear end pivotally mounted relative
to a loading dock to provide movement of the deck between the
stored position and a range of operative positions, and a lip
pivotally connected to the deck at the front end for pivotal
movement between a pendant position and an extended position
wherein the lip may engage the vehicle. The dock leveler also
includes at least one leg member or safety leg pivotally connected
to the front end of the deck, preferably about the same pivot as
the lip. The leg is pivotal between a supporting position, wherein
the leg is disposed to arrest downward movement of the deck, such
as by engaging a stop, and a nonsupporting position. In a preferred
embodiment of the invention, the mounting of the leg member at or
adjacent to the front end of the deck allows the leg member to be
pivoted forward (i.e., the free end of the leg moving away from the
rear end of the deck) as it moves to the nonsupporting position.
The leveler also includes a leg control member or sensor member,
also pivotally attached adjacent or at the front end of the deck,
and also preferably pivoted about the same hinge as the lip and the
leg member. Further, the leg control member or sensor preferably
forms a part of the lip itself. The sensor is adapted to engage the
bed of the vehicle along with the lip, and to maintain the leg
member in a nonsupporting position, so long as the sensor is
carried on the bed of the vehicle. The sensor is also adapted to
lose contact with a departing vehicle before the lip loses contact
with the vehicle. This loss of contact between the sensor and the
vehicle bed allows the leg member to return to a supporting
position, such that downward movement of the deck will be arrested
in the event the vehicle continues departing and the lip loses
contact with the bed of the vehicle with a load present on the
deck.
According to one embodiment of the invention, the sensor is carried
by the lip, such that movement of the lip from a pendant to a
extended position moves the sensor between its pendant position and
a first position. In this embodiment, that first position is an
extended position, but wherein the sensor is disposed below the
lip, such that the sensor will contact the bed of the vehicle
before the lip does, as the leveler is pivoted downward. The
connection between the lip and the sensor is a lost motion
connection such that contact of the bed by the sensor moves the
sensor relative to the lip until the sensor and lip are essentially
coplanar and resting on the bed of the truck. Movement of the
sensor from its first position to this second position retracts the
legs to the nonsupporting position by means of a connection between
the legs and the sensor member. As the vehicle departs, the sensor
member will lose contact with the bed of the vehicle before the lip
loses contact with the bed of the vehicle. The lost motion
connection between the lip and the sensor allows the sensor to move
from the second position back to the first position, thus restoring
the leg member to a supporting position such that, for subsequent
disengagement between the lip and vehicle bed, the leg will be in a
supporting, deck-arresting position.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a dock leveler including a safety
leg assembly according to one embodiment of the present
invention;
FIGS. 2 and 3 are prior art drawings showing dock levelers with
safety leg assemblies that exhibit stump out;
FIGS. 4-8 are a series of operational section views of the dock
leveler according to the invention and shown in FIG. 1;
FIG. 9 is a front elevation of a dock leveler according to the
invention, shown in the operational configuration of FIG. 6;
FIG. 11 is the dock leveler of FIG. 1, shown in a side section, and
showing a below dock end load configuration;
FIG. 11 an alternative embodiment of the invention, showing a
modified pedestal;
FIG. 12 is a further alternative embodiment of the invention,
showing a modified pedestal;
FIG. 13 is a perspective view of a dock leveler according to an
alternative embodiment of the invention;
FIG. 14 is a side section of the leveler of FIG. 13;
FIG. 15 is a side section view of a dock leveler according to an
alternative embodiment of the invention; and
FIG. 16 is a side section view of a dock leveler according to a
further alternative embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A dock leveler according to a first embodiment of the invention is
seen in perspective view in FIG. 1. As in conventional dock
levelers, the leveler 10 according to the invention includes a deck
12 that is pivotally connected relative to a loading dock. In this
embodiment, the leveler deck 12 is pivotally connected at its rear
end (not shown) to framing members (not shown) typically disposed
in a pit P formed at the loading dock with which the leveler is
associated (the pit P can be seen in the side elevational drawings
of FIGS. 4-8). This allows the deck to pivot between a
cross-traffic position (FIG. 4) and a range of operative positions
(FIGS. 5-8) including a preparatory position (FIG. 5) at which the
deck is pivoted upward to its greatest extent.
The deck can be moved through its various positions by means of a
variety of actuators such as those described in the background
section (i.e., springs, hydraulic cylinder, or other actuators). A
specific example of actuation can be found in U.S. Pat. No.
5,440,772 the teachings of which are expressly incorporated herein
by reference. The deck 12 may be reinforced and supported by side
members 13, and by a header member 14 disposed between the side
members adjacent the front end of the deck 12. A lip 21 is
pivotally attached adjacent the front end of the deck 12 about
hinge 11. At least one leg control member or sensor 25 (this
embodiment shows two sensors 25) is disposed laterally of the lip
21, and is disposed for pivotal movement on the same hinge 11 as
the lip 21. The sensor 25 is preferably shorter in length than the
lip 21, as will be described in greater detail below. It forms an
aspect of the invention that both the lip 21 and the sensor or
sensors 25 are pivotally connected about a common hinge 11.
Further, as sensors 25 are disposed laterally of lip 21, and as
they are disposed about a common hinge, sensors 25 and lip 21 may
be considered as individual pieces of a single lip structure 20
that includes a main section (lip 21) and a sensor section or
sections (sensor or sensors 25).
To support the deck 12 in a cross-traffic position, and/or to
arrest downward movement of the deck in a free-fall situation, at
least one leg member 30 is included. In the present embodiment, a
pair of leg members 30 are joined by a connecting strut 32. In
turn, each of the leg members (or "safety legs") 30 is pivotally
attached adjacent the front end of the deck 12. In the present
embodiment, the legs 30 are pivotally attached to the same hinge 11
as the lip 21 and leg control member or sensor 25. Alternatively,
leg or legs 30 could be disposed elsewhere adjacent the front end
of the deck 20, such as below the hinge 11 on a separate hinge 33
shown in FIGS. 15 and 16, to be discussed in greater detail below.
The pivotal mounting of the legs 30 allows them to pivot between a
supporting position, such as is shown in FIGS. 4 and 5, and a
non-supporting position as shown in FIG. 6. In a supporting
position, leg 30 is disposed such that it will engage a stop member
or pedestal 40 disposed within the pit P as the deck pivots
downward due to downward forces exerted on the deck 12. Pedestal
40, in the present embodiment, includes more than one support
surface 42 for receiving the leg 30 when in a supporting position.
Accordingly, the supporting "position" may actually be a range of
positions. Similarly, the leg 30 may also pivot to a non-supporting
position, such as that shown in FIG. 6. In the non-supporting
position (or within the range of non-supporting positions), the leg
30 is disposed to not engage the pedestal 40 to arrest downward
movement of the deck. The non-supporting positions of the leg 30
are often referred to as "retracted" positions. With the leg or
legs 30 in this retracted or non-supporting position, free fall of
the deck 12 would not be prevented in the event of unscheduled or
unintended departure of the vehicle being loaded or unloaded with a
forklift or other load present on the deck 12. However, the ability
to move the leg 30 to a retracted position allows the problem of
stump out, described above, to be avoided during the normal loading
and unloading operation, i.e., with the vehicle parked, and lip 21
engaging the bed B of the vehicle.
As it is thus desirable to be able to retract the leg 30 to prevent
stump-out during normal operation and to still have the leg 30 in a
supporting position to prevent an uncontrolled free-fall situation,
the dock leveler according to the present embodiment provides both
of these functions. The lip 21 and sensor 25 are interconnected
with the leg 30 in a manner to provide both for retraction of the
leg 30 during normal operation of the leveler, and for movement of
the leg 30 to a supporting position before the vehicle departs, to
prevent uncontrolled free fall. This structure and advantageous
function will be described in reference to FIGS. 4-8, representing
an operational sequence of dock leveler operation. FIG. 4 shows the
dock leveler 10 in a stored, cross-traffic position. In FIG. 5, the
deck 12 has been raised to a preparatory position, causing the lip
21 and sensor 25 to be extended. In FIG. 6, the deck 12 has been
lowered, such that the lip 21 and sensor 25 engage the bed B of the
parked vehicle to provide the normal loading and unloading
operation. FIG. 7 represents a departure situation, with the bed B
of the vehicle moving away from the loading dock. FIG. 8 shows the
vehicle bed B fully departed such that the lip 21 completely loses
contact with the vehicle.
In the present embodiment, the coupling between the lip 21 and the
sensor 25 is in the form of a bracket member 70 disposed at a
lateral edge of the lip 21 (two such members are shown in FIG. 1 as
it includes two sensors 25). The bracket 70 has a general L-shape
including a lug 72 that engages the underside of the sensor 25.
Accordingly, the bracket 70 allows the lip 21 to "carry" the sensor
25. That is, as the lip 21 moves between its pendant position (FIG.
4) and an extended position (FIG. 5), the sensor 25 is moved
between its pendant position (FIG. 4) and a first position (FIG. 5)
disposed beneath the lip 21. With the lip 21 thus extended and the
sensor 25 in the first, or preparatory position, the deck is now
ready to be lowered onto the bed B of the vehicle. As the deck is
lowered, the lip 21 engages the bed. In this embodiment, the sensor
25 first engages the bed B of the vehicle. Because of the lost
motion nature of the coupling between the lip 21 and the sensor 25,
the sensor is allowed to move relative to the lip 21 to a second
position, shown in FIG. 6, wherein the sensor 25 is substantially
flush with the lip 21, and wherein both the sensor 25 and the lip
are resting on the bed B of the vehicle.
The coupling between the sensor 25 and the leg member 30 is similar
in this embodiment, as it is in the form of a bracket member 80
including a lug 82 that engages the back side of the leg member 30.
The spacing of the lug 82 from the sensor 25 is such that the
sensor moves from its pendant position (FIG. 4) to the first
position (FIG. 5) without moving or retracting the leg 30. Thus,
with the lip 21 extended and the sensor 25 in the first position
(FIG. 5), the leg 30 remains in a supporting position. As the
sensor 25 engages the bed B of the vehicle and rotates to the
second position (FIG. 6), the leg member 30 is moved by the bracket
80 to a nonsupporting or retracted position. Thus, with the lip 21
and sensor 25 disposed on the bed B of the vehicle, the leg member
is in a retracted position, allowing the deck 12 to move up and
down with the bed B of the vehicle through the full operating range
of the leveler without stump-out occurring. Since the sensor 25 in
the present embodiment controls whether the leg member 30 is in a
supporting or nonsupporting position, it may also be referred to
herein as a leg control member.
At the same time, the structure of and the couplings between the
lip 21, sensor 25 and leg member 30 also provide for free-fall
protection in the event of premature vehicle departure with a load
present on dock 12. With the sensor 25 on the bed B of the vehicle,
the sensor 25 is spaced from the lug 72 of the bracket 70, but the
leg member 30 is adjacent to or contacting the lug 82 of the
bracket 80. Upon departure of the vehicle being serviced, and
because the length of the sensor 25 is shorter than the length of
the lip 21, the sensor 25 will lose contact with the vehicle before
the lip 21 loses contact with the vehicle (FIG. 7). When this
occurs, the sensor 25 moves relative to the lip 21 and back to the
first position, until it engages the lug 72. As the sensor 25 moves
back to the first position, the leg member 30 is returned to a
supporting position. While the nature of the couplings between the
lip 21, the sensor 25 and the leg member 30 are such that gravity
will return the legs to a supporting position once the sensor 25
loses contact with the bed B, a biasing member such as spring 90
may be employed to bias the leg member 30 toward a supporting
position. The spring 90 will decrease the time required to return
the leg 30 a to a supporting position, as compared to relying on
gravity alone for this function. Thus, as can be seen in FIG. 7,
the leg member has been returned to a supporting position prior to
the lip 21 losing contact with the bed B of the vehicle. FIG. 8
then shows the vehicle fully departed, and the lip 21 losing
contact with the bed B.
The dock leveler according to this embodiment of the invention thus
provides for normal operation without stump-out, since the leg
member 30 is held in a retracted or non-supporting position so long
as the sensor 25 remains on the vehicle. Upon departure of the
vehicle, but prior to the lip 21 losing contact with the vehicle,
the leg member 30 is returned to a supporting position. If a load
is then present on the deck when a vehicle is fully departed (lip
21 loses any contact with the vehicle), the leg member 30 will be
in a supporting position to prevent uncontrolled free fall. The
dock leveler according to the invention provides this advantageous
function by providing the lip 21 and the leg member or members 30
on a common hinge 11. Since the various components controlling the
leg member 30, as well as the leg member 30 itself, do not have to
be mounted on their own pivot axes (as in prior attempts to provide
similar function), the reliability and manufacturability of this
design is improved. Further, the function is also provided by
preferably making the sensor 25 a part of a lip structure 20, as
opposed to being a separate and separately-mounted member. Further
still, the mounting of the leg member 30 adjacent the front end of
the deck (in this case on the hinge 11) allows the leg member 30 to
be rotated forward when moving from a supporting to a
non-supporting or retracted position. This allows a smaller
necessary range of movement for the leg member 30, since it must
only be moved far enough forward to avoid contact with the pedestal
40. In designs where the legs were retracted "back," they not only
had to clear a pedestal, but had to be retracted far enough back
and up so as to not contact the pit or leveler framing when the
deck was in a below-dock position.
The dock leveler according to the invention also includes structure
for providing for below-dock end load. A below-dock end load is a
loading or unloading situation wherein cargo is being loaded or
unloaded from the extreme rear end of the vehicle bed. As a result,
there is no available bed upon which to place to lip of the dock
leveler. Accordingly, the leveler is used as a ramp without the lip
extended, with the fork truck or other material handling vehicle
simply driving to the end of the deck and "picking" the end load
(or placing it in the case of loading) from the bed of the vehicle.
Performing an end load above dock height does not present
particular problems. However, a below-dock end load with a dock
leveler including safety legs requires that the legs be retracted
to allow the deck to go below-dock without the legs engaging the
stops or pedestals. In the present embodiment, a retracting
mechanism 100 is provided to perform this function. A bar linkage
100 comprising first (105) and second (110) links is connected
between the deck and the leg member 30. As seen most clearly in
FIG. 1, in this case the bar linkage is connected to the strut 32
connecting the two leg members 30. The linkage is actuated by a
pull-chain 115. As the chain is pulled upwards by an operator
standing on the deck 12, the linkage toggles, exerting an outward
force on the leg member 30 tending to rotate it forward. This
rotational force on the leg member 30 causes the leg member 30 to
push on the lip 21, also rotating it and sensor 25 outward. With
the leg member 30 retracted in this manner, a below-dock end load
can be performed. Operationally, the dock leveler would start in
the cross-traffic position of FIG. 4. The main pull chain would be
pulled briefly to release the holddown and allow the deck to raise
slightly, such that the lip 21 is not contacting the pedestal 40,
but not far enough up such that the lip 21 is extended. The
operator then walks forward on the deck 12, pulling pull-chain 115
to retract the legs. As he walks further out on the deck 12, it
rotates downward to a below-dock position shown in FIG. 10. The end
load can now be performed. Once the chain 115 is released, the leg
member 30 will tend to rotate back to a supporting position, either
by gravity, or under the effect of the biasing member 90. Of
course, it will be appreciated by one of skill in the art that the
same linkage 100 may be used to retract legs 30 to allow normal
(i.e. non-end-load) servicing of vehicles initially disposed below
dock height.
It will be noted that the pedestal 40 shown in FIGS. 4-8 includes a
plurality of stops, in this case first stop 42 and second stop 43.
Multiple stops are included so that, for a free-fall situation, a
stop will be disposed within a small distance from the end of the
leg member 30 so that the maximum distance of the free fall will be
limited. The larger the number of stops, the smaller the maximum
distance of free fall. For example, instead of the two steps shown
in FIGS. 4-8, three stops could be used, as shown in FIG. 12. As
will be appreciated by one of skill in the art, geometries and
spacing may limit the number of stops that may practically be
included on the pedestal. Further, the pedestal 40 may be provided
with a lipkeeper 130 as in FIG. 11. The lip 21 is disposed behind
the lipkeeper 130 when the dock leveler 10 is in the stored, or
cross-traffic position. The lipkeeper 130 prevents the lip from
being pulled out with the leveler in a cross-traffic position,
which could represent a security issue, since an intruder could
lower the leveler with the lip extended and enter the building
through the gap between the building door and the deck. It should
also be noted that although the dock leveler is shown in FIG. 4 as
resting on the lip 21 in the cross-traffic position, the leg member
30 could alternatively be engaged on the pedestal 40 to support the
weight of the deck in this position.
FIGS. 13-16 show alternative embodiments of the invention. Since
components are similar to the embodiment shown in FIGS. 4-12, the
same reference numbers with a prime (') designation will be used.
These embodiments do not include members for sensing the departure
of the vehicle, nor for retracting the leg member for normal
operation. They do show, however, the advantageous feature of
disposing the leg member adjacent the front end of the deck 12,
illustratively either on the same hinge 11' as the lip 21' (FIGS.
13 and 14), or disposed at the front end of the deck 12, but on a
separate hinge 33 disposed beneath the lip hinge 11'. The structure
and operation of the leg member 30' in FIGS. 13 and 14 is the same
as that in FIGS. 4-8, but without the ability to retract the leg
member 30' for normal operation without stump-out. A bar linkage
100' is provided to retract the leg member 30' for below-dock
service. The leg member 30' shown in FIG. 15 is also similar in
operation, but disposed on a hinge 33 beneath the main hinge 11'.
The leg member 30' of FIG. 16 is slightly different in that it is
intended to be retracted rearwardly for a below-dock end load.
Toward that end, pull-chain 115' is connected directly to the leg
member 30' at a lug 116. A compression spring 170 is shown disposed
between the leg member 30'and the header 14' tends to rotate the
leg member 30' back to a supporting position once the chain 115' is
released. A stop member 180 is also disposed on the header 14' to
limit the forward rotation of the leg member 30', and maintain it
in a supporting position.
There has thus been disclosed a dock leveler including a safety leg
assembly that prevents stump out from occurring, while providing
protection against uncontrolled free fall. While embodiments of the
invention have been disclosed herein, such embodiments are not
intended to be limiting of the scope of the claimed invention.
Rather, the invention claimed encompasses all improvements,
modifications, or equivalents to these embodiments, or components
thereof, as may fall within the scope of the following claims.
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